Method of coating gelatin capsules with ethyl cellulose



April 3, 1957 J. T. CARSTENSEN ETAL 2,789,920

METHOD OF COATING GELATIN CAPSULES WITH ETHYL CELLULOSE Fild Deb.

Y Y 295 3 @555 mmmuxm 5533 833mm 3R3? 3% 5.653: m qmbmi mfi a: 4 SE 3 2 $3 Ffi x v31 5 E G1 33 S u s IN VEN TOR}; JENS THUROE CARS TEN EN KENNETH WIL BUR KNIGHT WILLIAM VALENTINE JOSEPH F FANG/S W E IDE NHE [HE R BY W M n A T TORNE Y- United States Patent 'METHOD OF CQATING GELATIN CAPSULES WITH ETHYL CELLULOSE Jens Thuroe Carstensen, Pearl River, N. Y., Kenneth Wilbur Knight, Franklin Lakes, N. 1., and William Valentine, Nanuet, and Joseph Francis Weidenhermer, Pearl River, N. Y., assignors to American Cyanamid Company, New York, N. Y., a corporation of Mame Application December 19,1955, Serial No. 553,735

3 Claims. (Cl. 117-55) This invention relates to a method of treating soft gelatin capsules to form a bright shiny coating on the surface of the capsules by first acid hydrolyzing the surface of the cap-sules until shiny, and then coating with ethyl cellulose, the acid treatment and coating being aided by a volatile organic solvent.

Soft gelatin capsules are formed by sealing together two sheets of a plasticized gelatinous mixture around suitable capsule contents. The gelatin film usually consists of gelatin together with plasticizers such as glycerin and water, although other plasticizers may also be present. These capsules may be filled with a powder, or a liquid, or both. A machine for forming such capsules, is described in a patent to F. E. Stirn et al. 2,697,317, Capsule Forming Die Roll, December 21, 1954. Gelatin capsules have been coated with gum benzoin, which may be co-deposited with a treatment by formaldehyde such as described in a U. S. patent to Yen et al. 2,727,833, Capsule Finishing Process, dated December 20, 1955.

In the finishing of capsules, particularly those which are powder filled, at times, defective capsules spill their contents onto the surface of the capsules, particularly if they are tumbled to insure a round configuration. The surface of the capsules may be rubbed sufiiciently that the contents stick to the surface of the gelatin and rather than a polished capsule, there is produced a dull capsule.

To place a shine on these dull capsules has been difficult as a thin coat of a polishing coat suchas gum benzoin does not produce as polished a capsule as is desired when used on dull or scarred capsules.

On such'dull capsules such a thick coating is required that the rate of the solution of the capsules on ingestion is altered.

It would thus seem that it is impossible to put a shiny surface on the coating of such a capsule. This is in fact the case, but it is an illusory limitation.

To form a shiny surface on these capsules, the surface of the capsules must first be made shiny and then a protective coating placed thereon. Surprisingly this may be readily accomplished by using a neutral, water miscible, volatile organic solvent solution of an acid which hydrolyzes and breaks down the gelatin structure at the surface of the capsules. This causes any imperfections to be smoothed out but, at the same time the surface of the capsules may become comparatively tacky because the degradation of the gelatin produces glue. Surprisingly, if before the capsules become stuck to each other, they are coated with a solvent solution of ethyl cellulose, there is deposited on the surface of the capsules a thin protective layer of ethyl cellulose, which is suficiently thick to keep the capsules from sticking to each other. This coat protects and accentuates the gloss on the surface of the capsules, and yet does not appreciably alter the solubility characteristics of the capsules in the intestinal tract.

Ethyl cellulose has been used to manufacture capsules as for example described in U. S. Patent 2,251,109 to Bratring, Method of Producing Highly Lustrous Hollow Bodies From Acetyl Cellulose and Like Plastic Substances.

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As contrastedwith such prior art capsules which are formed from ethyl cellulose, the present coating of ethyl cellulose on the surface of the gelatin capsules is so. thin that it does not cause a measurable change in the rate of ingestion of the capsules, and accordingly, comparatively rapidly dissolving capsules may be easily produced which are glossy and acceptable to the pharmaceutical profession.

The accompanying drawing shows ingraphic form the present process.

In the initial step, or' shining step a neutral, watermiscible, volatile organic solvent such as the lower alkanols, including methanol, ethanol, and propa'nols, dioxan, acetone, methyl-ethyl ketone, diacetone, lower 'alkoxy alkanols, such as Z-methoxy-etlranol and Z-ethoxyethanol and their mixtures, is used as a solvent for hydrochloric acid and some water. The acid maybe diluted before mixing with the water-miscible, volatile organic solvent, in which case additional water need not be-added. A 4-6 carbon alcohol is preferred as the solvent for the coating step. Commercially available mixed amyl alcohols are usually most economical.

The acid treatment should he comparatively short in order that only the surface of the capsules is degraded and turned to a tacky material. From 0.025 to 5% of concentrated hydrochloric acid and from 1 to 10% of water in the neutral, water-miscible, volatile organic solvent is preferred, with the time of treatment inversely proportional to the acid concentration. Around 30 seconds is long enough with 5% of hydrochloric acid, and 24 hours may -be used with 0.025% of hydrochloric acid. This produces agloss on the surface which is immediately protected by the coating solution.

It is preferred thatthe ethyl cellulose be present in a concentration of about2 to 7% in an alcoholic organic solvent, with particularly effective results being obtained with a 4% concentration of a low viscosity grade of ethyl cellulose in a mixture of amyl alcohols. Pure amyl alcohols or theirmixtures may be used, but the commercial mixtures are more economical.

The capsules are conveniently treated by dipping them in (1) the shining solution and (2) the coating solution; however, they may also be conveniently shined by treating them in a polishing pan, such as is used in coating tablets.

The capsules coated by this procedure have a thickness of the ethyl cellulose of less than half a thousandth of an inch. The exact thickness is diflicult to determine because the ethyl cellulose in part penetrates into the surface of the gelatin, which has been degraded, so that it sticks tightly, and because it is so thin, no convenient method of measuring is known. The thickness can be estimated from the amount of coating solution which remains on the surface of the capsules in the coating of the capsules in a coating pan, however, at least part of the ethyl cellulose adheres to the pan itself as usually a muslin lined pan is used, and accordingly, the thickness is something less than half a thousandth of an inch.

When tested for disintegration time, it is found that by the standard U. S. Pharmacopoeia method, the disintegration time with the regular gum benzoin coating is 5 minutes as described in the above mentioned Yen patent, and the disintegration time when coated with a 3% ethyl cellulose in amyl alcohols is 5 minutes, and when coated with a 5% ethyl cellulose in amyl alcohols is still 5 minutes. The water solubility and gastric juice solubility are not altered by the present polishing treatment.

The following examples illustrate embodiments of our invention:

Example 1 5000 capsules containing dibasic calcium phosphate, among other constituents (which had become dull by the spilling of part of the encapsulated powder on the surface of the capsules) were first shaken to remove excess powder, and then dipped for /2 minute in a bath containing by weight of hydrochloric acid and 5% of water in isopropanol. The capsules were allowed to drain for another 30 seconds, and then dipped into a coating solution containing 3% low viscosity ethyl cellulose in commercial amyl alcohol. The capsules were removed from the solution and spun dry in a basket centrifuge to throw off the excess coating liquid, and to evaporate the solvent from the capsules. Spinning for 5 minutes completed the drying. The capsules were shiny, free from blemishes, showed no blisters, and no twinning, a defect in which certain of the capsules stick to each other so that they form multiple twins.

Example 2 5000 capsules were placed in a muslin lined tablet polishing pan. 25 milliliters of solution containing 5% by volume of concentrated hydrochloric acid, 5% by volume of water, and the remainder ethanol were added to the coating pan a little at a time. The amount added in each increment was such that the capsules just started to slide on the inside of the pan, in accordance with conventional coating processes. After all coating solution had been applied the capsules were rotated in the pan until the solvent had evaporated, and then was added 50 milliliters of a coating solution consisting of 3% ethyl cellulose in butanol. The coating solution was added a little at a time so that the capsules just started to slip in the pan in accordance with conventional coating procedures, and air was circulated through the pan to evaporate the solvent. After all of the coating solution was added, air was circulated until the solvent evaporated. The capsules were then dumped out onto trays and inspected.

The capsules were found to be shiny, free from blemishes, and non-tacky so that they did not stick to each other on storage. The capsules so coated 'had a disintegration time of 5 minutes in accordance with the standard U. S. Pharmacopoeia test.

Example 3 5000 capsules were shined by the process of Example 1 using a shining solution containing 5% concentrated hydrochloric acid and 5% water in acetone. The coating solution was 3% low viscosity ethyl cellulose in hexanol. Shiny, blemish-free capsules were produced which had unaltered solubility characteristics.

4 Example 4 5000 dull capsules were dipped in a bath containing 7 /2% concentrated hydrochloric acid and 2 /2% water in Z-ethoxy-ethanol for /2 minute, the capsules shaken and allowed to drain for about /2 minute, and then dipped in a 5% solution of ethyl cellulose in pentanol. The capsules were removed from the solution, and spun for 5 minutes in a basket centrifuge to dry. The capsules were shiny and free from blemishes.

Example 5 5000 dull capsules were agitated for 2 minutes in a shining bath consisting of 2 /2% concentrated hydrochloric acid and 7 /2% water in dioxan, the capsules were removed, shaken to remove the excess-shining solution and then dipped in a 3% solution of ethyl cellulose in a commercial mixture of amyl alcohols. The capsules were removed, and dried with agitation in a blast of warm air. The capsules were shiny and free from blemishes.

We claim:

1. A method of producing shining soft gelatin capsules which comprises contacting dull-surfaced soft gelatin capsules with a solution of 0.025 to 5% concentrated hydrochloric acid and from 1 to 10% water in a neutral, water-miscible, volatile, organic solvent in which aqueous hydrochloric acid is soluble until a shine is imparted to the surface of the capsules, separating the capsules from said solution and immediately, while still wet, contacting the thus shined capsules with a 2 to 7% solution of ethyl cellulose in a 4 to 6 carbon alcohol, draining and drying the solvent on the surface of the capsules.

2. The method of claim 1 in which the capsules are dipped in both the neutral, water-miscible, volatile, organic solvent-water-hydrochloric acid solution, and the alcoholic ethyl cellulose solution.

3. The method of claim 1 in which the capsules are tumbled, the neutral, water-miscible, volatile, organic 'solvent-water-hydrochloric acid solution added, the solvent evaporated, and the alcoholic ethyl cellulose solution is added to the tumbled capsules, and the solvent evaporated.

References Cited in the file of this patent UNITED STATES PATENTS 2,065,792 Charch Dec. 29, 1936 2,578,943 'Palermo Dec. 18, 1951 2,600,367 Stirn June 10, 1952 2,727,833 Yen Dec. 20, 1955 

1. A METHOD OF PRODUCING SHINING SOFT GELATIN CAPSULE WHICH COMPRISES CONTACTING DULL-SURFACED SOFT GELATIN CAPSULES WITH A SOLUTION OF 0.025 TO 5% CONCENTRATED HYDROCHLORIC ACID AND FROM 1 TO 10% WATER IN A NEUTRAL, WATER-MISCIBLE, VOLATILE, ORGANIC SOLVENT IN WHICH AQUEOUS HYDROCHLORIC ACID IS SOLUBLE UNTIL A SHINE IS IMPARTED TO THE SURFACE OF THE CAPASULES, SEPARATING THE CAPSULES FROM SAID SOLUTION OF THE CAPSULES, SEPARATING THE CAPSULES TACTING THE THUS SHINED CAPSULES WITH A 2 TO 7% SOLUTION OF ETHYL CELLULOSE IN A 4 TO 6 CARBON ALCOHOL, DRAINING AND DRYING THE SOLVENT ON THE SURFACE OF THE CAPSULES. 